This diamond-shaped lump of rock is a so-called E-type asteroid with a diameter of roughly 4.6 km that orbits the sun in the main asteroid belt between Mars and Jupiter. Šteins was discovered in 1969 by Lithuanian astronomer Nikolay Chernykh (1931–2004), and was named after the Latvian astronomer and science communicator Kārlis Šteins (1911–1983).
My interest in Rosetta derives partly from the year I spent working at ESA’s operations centre in Darmstadt on interplanetary spacecraft navigation.
Visible in the mosaic above are a number of small craters on the asteroid, and two large craters of around 2 km in diameter. The presence of such structures indicates that the body is very old.
The animation shows the spacecraft’s closest approach to Šteins, starting three minutes before at a distance of 2000 km, and ending four minutes after closest approach.